Ultrasonic Spraying Coating Machine For Battery Electrodes

What are battery electrode coating materials?

Battery electrode coating materials refer to the functional material systems coated on the surface of the battery current collectors (positive electrode aluminum foil, negative electrode copper foil), constituting the core electrochemical active areas of the battery. They mainly exist in slurry or solution form and directly determine key indicators such as battery capacity, cycle life, and rate performance.

1. Core Classification and Composition
Positive/Negative Electrode Active Coating Materials: The most crucial coating materials, forming the main body of the electrochemical reactions during battery charging and discharging.

Common Positive Electrode Materials: Active materials such as ternary materials (NCM), lithium iron phosphate (LFP), and lithium cobalt oxide (LCO), mixed with conductive agents (such as carbon black, CNT), binders (such as PVDF), and solvents (such as NMP) to form a slurry.

Common Negative Electrode Materials: Active materials such as graphite, silicon-based materials, and hard carbon/soft carbon, combined with conductive agents, binders (such as SBR), thickeners (such as CMC), and deionized water to form an aqueous slurry.

2. Key Performance Requirements

Suitable viscosity (typically 10-100 cP) and dispersion stability are required to prevent agglomeration or sedimentation during spraying.

The content of active materials and particle size must be precisely controlled to ensure the electrochemical activity and structural uniformity of the coating.

 

Strong adhesion to the current collector, it should not easily peel off after drying and curing, while also possessing a certain degree of flexibility to adapt to electrode rolling processes.

 

How is ultrasonic atomization spraying used for battery electrode coating materials?

When ultrasonic atomization spraying is used for battery electrode coating materials, it requires three core steps: initial material adaptation, intermediate parameterized spraying, and final curing treatment. It is suitable for various electrode coating materials, including positive and negative electrode active coatings and surface modification coatings. The specific process and key points are as follows: Initial Preparation: Material Preparation for Atomization Battery electrode coating materials are mostly slurries containing a mixture of active materials, conductive agents, and binders, or catalyst solutions, solid electrolyte slurries, etc., which need to be adjusted to a state suitable for ultrasonic atomization. First, adjust the viscosity and surface tension. The slurry viscosity should typically be adjusted to below 30 cP. If necessary, add appropriate solvents or surfactants to avoid excessively high viscosity affecting atomization or too low viscosity causing coating runoff. Second, ensure uniform particle dispersion. For slurries containing nano-sized active particles or catalyst particles, ultrasonic dispersion pretreatment and the addition of suitable dispersants are required to prevent particle agglomeration and sedimentation, thus avoiding impact on coating performance. Third, optimize the solvent ratio by selecting a solvent combination with suitable evaporation rates to balance the drying speed of droplets during flight. This prevents premature drying of droplets, resulting in "dry spraying," and also ensures effective leveling and film formation on the current collector.

Core Spraying: Parametric Precision Deposition. This step involves adjusting equipment parameters to atomize and precisely deposit the adapted coating material onto the current collector, adapting to different electrode coating requirements:
Material Atomization and Transport: The ultrasonic nozzles of the equipment use high-frequency vibrations of 20kHz - 120kHz to "tear" the coating material into uniform droplets of 10-50 micrometers. Simultaneously, the use of low-pressure carrier gas not only guides droplets to form a stable atomized cone shape, preventing droplet aggregation near the nozzle, but also assists in solvent evaporation, avoiding material splashing problems associated with traditional high-pressure spraying.

 

Precise Deposition Control: By adjusting spraying parameters to match different coating requirements, such as adjusting the liquid supply rate and nozzle movement speed, the loading of active material on the current collector can be controlled; adjusting the distance between the nozzle and the current collector prevents droplet agglomeration or premature drying, ensuring deposition effectiveness. For example, in cathode catalyst spraying, submicron-level ultrathin coatings can be precisely prepared; in solid-state battery electrode spraying, temperature-sensitive solid electrolyte slurry films can be formed through low-temperature processes. Furthermore, the equipment can control the nozzle trajectory via a three-axis sliding platform to achieve nanometer-level precision surface modification coating spraying.

 

Post-Processing: Curing and Shaping Ensures Performance. The coated electrodes require drying and subsequent processing to ensure stable coating adhesion and optimal performance. The drying process requires strict control of temperature and time to avoid cracking of the electrode material and changes in the performance of the active material caused by high temperature or rapid drying. For some electrodes, moderate compaction is performed after drying to further increase the electrode density, while the compaction force must be controlled to prevent damage to the coating structure. For solid-state battery electrodes, this low-temperature post-treatment process can also avoid the decomposition of the solid electrolyte caused by high-temperature sintering, and optimize the interface bonding state between the electrode and electrolyte.

 

How to ensure the uniformity of battery electrode coating materials?

Ensuring the uniformity of battery electrode coating materials is mainly achieved through three dimensions: the stability of the material itself, precise control of the spraying process, and compatibility of the substrate with the environment. This is achieved through closed-loop management throughout the entire process. Specific key measures are as follows:

1. Material pretreatment: Preventing coating defects from the source.

Optimizing slurry dispersibility: Using a combination of "high-speed shearing + ultrasonic dispersion" to break up agglomerated particles of active material and conductive agent, controlling the particle size distribution to be uniform (typically D50 is 1-5μm).

Stabilizing Slurry Characteristics: Precisely controlling viscosity (10-100 cP) and surface tension, adding an appropriate amount of dispersant to prevent particle sedimentation, and maintaining slurry homogeneity through continuous low-speed stirring to avoid concentration fluctuations during spraying.

Filtering Impurities and Air Bubbles: Filtering the slurry with a 200-500 mesh screen to remove large particles; performing vacuum degassing before spraying to prevent pinholes and missed areas in the coating caused by air bubbles.

 

2. Spraying Process: Precise Control of Deposition Consistency

Refined Equipment Parameters: The ultrasonic nozzle frequency is fixed at 20-120 kHz to ensure uniform droplet size (10-50 μm); a closed-loop system controls the liquid supply rate (0.1-5 mL/min) and nozzle movement speed (1-10 mm/s) to ensure consistent material load per unit area.

Substrate and Nozzle Adaptation: Maintain a stable distance (5-20mm) between the nozzle and the collector (aluminum foil/copper foil). Control the nozzle trajectory using a three-axis linkage platform to avoid edge overflow or excessive thickness in the center. Use constant tension control for collector transfer to prevent substrate wrinkles from causing uneven coating.

Segmented Compensation Adjustment: Set parameter compensation (e.g., fine-tune the liquid supply speed) at the head and tail of the electrode to avoid coating thickness deviations during start-up and shutdown. Use an online thickness gauge for real-time feedback to dynamically adjust spraying parameters.

 

3. Environment and Post-treatment: Ensure Stable Coating Formation

Control the Spraying Environment: Maintain a workshop temperature of 20-25℃ and relative humidity of 40%-60% to avoid temperature fluctuations causing uneven solvent evaporation rates, which can lead to coating sagging or cracking.

Optimized Drying and Curing: Use segmented drying (pre-drying + final drying) to control the heating rate and avoid uneven coating shrinkage caused by rapid local drying. After drying, inspect the electrode for flatness and discard any warped or wrinkled products.